Low temperature growth of ultrananocrystalline diamond

Abstract

Ultrananocrystalline diamond (UNCD) films were prepared by microwave plasma chemical vapor deposition using argon-rich $\mathrm{Ar}∕{\mathrm{CH}}_4$ plasmas at substrate temperatures from $\sim 400$ to $800°\mathrm{C}$ . Different seeding processes were employed to enhance the initial nucleation density for UNCD growth to about ${10}^{11}\mathrm{sites}∕{\mathrm{cm}}^2$ . High-resolution transmission electron microscopy, near-edge x-ray absorption fine structure, visible and ultraviolet Raman spectroscopy, and scanning electron microscopy were used to study the bonding structure as a function of growth temperature. The results showed that the growth of UNCD films is much less dependent on substrate temperature than for hydrogen-based ${\mathrm{CH}}_4∕{\mathrm{H}}_2$ plasmas. UNCD with nearly the same nanoscale structure as those characteristic of high-temperature deposition can be grown at temperatures as low as $400°\mathrm{C}$ with growth rates of about $0.2\mathrm{\mu }\mathrm{m}∕\mathrm{hr}$ . The average grain size increased to about $8\mathrm{nm}$ from $3$ to $5\mathrm{nm}$ that is characteristic of high-temperature growth, but the relative amounts of $s{p}^3$ and $s{p}^2$ bonding remained unchanged. These results suggest that the activation energy for UNCD growth is about $2–3\mathrm{Kcal}∕\mathrm{mole}$ compared with $\sim 28\mathrm{kcal}∕\mathrm{mole}$ for traditional growth chemistries, and that hydrogen plays an important role in the growth of UNCD films using hydrogen-poor plasmas.